Method and system for silosilazanes, silosiloxanes, and siloxanes as additives for silicon dominant anodes

ABSTRACT

Systems and methods for silosilazanes, silosiloxanes, and siloxanes as additives for silicon-dominant anodes in a battery that may include a cathode, an electrolyte, and an anode active material. The active material may comprise 50% or more silicon as well as an additive including one or more of: silosilazane, silicon oxycarbides, and polyorganosiloxane. The silosilazane may comprise one or more amine groups, silanols, silyl ethers, sylil chlorides, dialkylamoinosilanes, silyl hydrides, and cyclic azasilanes. The active material may comprise a film with a thickness between 10 and 80 microns. The film may have a conductivity of 1 S/cm or more. The active material may comprise between 50% and 95% silicon. The active material may be held together by a pyrolyzed carbon film. The anode may comprise lithium, sodium, potassium, silicon, and/or mixtures and combinations thereof. The battery may comprise a lithium ion battery. The electrolyte may comprise a liquid, solid, or gel.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

N/A

FIELD

Aspects of the present disclosure relate to energy generation andstorage. More specifically, certain embodiments of the disclosure relateto a method and system for silosilazanes, silosiloxanes, and siloxanesas additives for silicon-dominant anodes.

BACKGROUND

Conventional approaches for battery anodes may be costly, cumbersome,and/or inefficient—e.g., they may be complex and/or time consuming toimplement, and may limit battery lifetime.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present disclosureas set forth in the remainder of the present application with referenceto the drawings.

BRIEF SUMMARY

A system and/or method for silosilazanes, silosiloxanes, and siloxanesas additives for silicon-dominant anodes, substantially as shown inand/or described in connection with at least one of the figures, as setforth more completely in the claims.

These and other advantages, aspects and novel features of the presentdisclosure, as well as details of an illustrated embodiment thereof,will be more fully understood from the following description anddrawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a battery with silicon-dominant anode withsilosilazane, silosiloxane, and/or siloxane additive, in accordance withan example embodiment of the disclosure.

FIG. 2 illustrates the general chemical structure of silosilazanes, inaccordance with an example embodiment of the disclosure.

FIG. 3A illustrates a process flow for fabricating a silicon-dominantanode with silosilazane additive, in accordance with an exampleembodiment of the disclosure.

FIG. 3B is a flow diagram of a process for direct coating electrodeswith silosilazane additive, in accordance with an example embodiment ofthe disclosure.

FIG. 4 illustrates a boxplot of anode conductivity of control anodes andanodes with silosilazane additive, in accordance with an exampleembodiment of the disclosure.

FIG. 5 shows an optical image of a silicon-dominant anode withsilosilazane additive, in accordance with an example embodiment of thedisclosure.

FIG. 6 illustrates cell swelling for control anodes and silosilazaneadditive anodes, in accordance with an example embodiment of thedisclosure.

FIG. 7 illustrates cycling performance for control silicon-dominantanode cells and silosilazane additive silicon-dominant anode cells, inaccordance with an example embodiment of the disclosure

FIG. 8 illustrates cycling performance with higher charge rate forcontrol silicon-dominant anode cells and silosilazane additivesilicon-dominant anode cells, in accordance with an example embodimentof the disclosure.

FIG. 9 illustrates cycling performance with a 4 C charge rate forcontrol silicon-dominant anode cells and silosilazane additivesilicon-dominant anode cells, in accordance with an example embodimentof the disclosure.

FIG. 10 illustrates cell performance with anodes comprising siliconpretreated with polysilosilazane, in accordance with an exampleembodiment of the disclosure.

FIG. 11 illustrates material characterization data for apolyorganosiloxane additive silicon-dominant anode, in accordance withan example embodiment of the disclosure.

FIG. 12 illustrates electrode conductivity for various silicon-dominantanodes with added silicon oxycarbides, in accordance with an exampleembodiment of the disclosure.

FIG. 13 illustrates cyclic voltammetetric analysis of half coin cellsfor different SiOC compositions, in accordance with an embodiment of thedisclosure.

FIG. 14 illustrates capacity retention of silicon-dominant anodes withpolyorganosiloxane and control anodes, in accordance with an exampleembodiment of the disclosure.

FIG. 15 illustrates conductivity of silicon-dominant control electrodesand electrodes with cyclic silosiloxane, in accordance with an exampleembodiment of the disclosure.

FIG. 16 illustrates cell performance for silicon-dominant anodes withpolydimethylsiloxane as an additive, in accordance with an embodiment ofthe disclosure.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a battery with silicon-dominant anode withsilosilazane, silosiloxane, and/or siloxane additive, in accordance withan example embodiment of the disclosure. Referring to FIG. 1, there isshown a battery 100 comprising a separator 103 sandwiched between ananode 101 and a cathode 105, with current collectors 107A and 1078.There is also shown a load 109 coupled to the battery 100 illustratinginstances when the battery 100 is in discharge mode. In this disclosure,the term “battery” may be used to indicate a single electrochemicalcell, a plurality of electrochemical cells formed into a module, and/ora plurality of modules formed into a pack.

The development of portable electronic devices and electrification oftransportation drive the need for high performance electrochemicalenergy storage. Small-scale (<100 Wh) to large-scale (>10 KWh) devicesprimarily use lithium-ion (Li-ion) batteries over other rechargeablebattery chemistries due to their high-performance.

The anode 101 and cathode 105, along with the current collectors 107Aand 107B, may comprise the electrodes, which may comprise plates orfilms within, or containing, an electrolyte material, where the platesmay provide a physical barrier for containing the electrolyte as well asa conductive contact to external structures. In other embodiments, theanode/cathode plates are immersed in electrolyte while an outer casingprovides electrolyte containment. The anode 101 and cathode areelectrically coupled to the current collectors 107A and 1078, whichcomprise metal or other conductive material for providing electricalcontact to the electrodes as well as physical support for the activematerial in forming electrodes.

The configuration shown in FIG. 1 illustrates the battery 100 indischarge mode, whereas in a charging configuration, the load 109 may bereplaced with a charger to reverse the process. In one class ofbatteries, the separator 103 is generally a film material, made of anelectrically insulating polymer, for example, that prevents electronsfrom flowing from anode 101 to cathode 105, or vice versa, while beingporous enough to allow ions to pass through the separator 103.Typically, the separator 103, cathode 105, and anode 101 materials areindividually formed into sheets, films, or active material coated foils.Sheets of the cathode, separator and anode are subsequently stacked orrolled with the separator 103 separating the cathode 105 and anode 101to form the battery 100. In some embodiments, the separator 103 is asheet and generally utilizes winding methods and stacking in itsmanufacture. In these methods, the anodes, cathodes, and currentcollectors (e.g., electrodes) may comprise films.

In an example scenario, the battery 100 may comprise a solid, liquid, orgel electrolyte. The separator 103 preferably does not dissolve intypical battery electrolytes such as compositions that may comprise:Ethylene Carbonate (EC), Fluoroethylene Carbonate (FEC), PropyleneCarbonate (PC), Dimethyl Carbonate (DMC), Ethyl Methyl Carbonate (EMC),Diethyl Carbonate (DEC), etc. with dissolved LiBF₄, LiAsF₆, LiPF₆, andLiClO₄ etc. The separator 103 may be wet or soaked with a liquid or gelelectrolyte. In addition, in an example embodiment, the separator 103does not melt below about 100 to 120° C., and exhibits sufficientmechanical properties for battery applications. A battery, in operation,can experience expansion and contraction of the anode and/or thecathode. In an example embodiment, the separator 103 can expand andcontract by at least about 5 to 10% without failing, and may also beflexible.

The separator 103 may be sufficiently porous so that ions can passthrough the separator once wet with, for example, a liquid or gelelectrolyte. Alternatively (or additionally), the separator may absorbthe electrolyte through a gelling or other process even withoutsignificant porosity. The porosity of the separator 103 is alsogenerally not too porous to allow the anode 101 and cathode 105 totransfer electrons through the separator 103.

The anode 101 and cathode 105 comprise electrodes for the battery 100,providing electrical connections to the device for transfer ofelectrical charge in charge and discharge states. The anode 101 maycomprise silicon, carbon, or combinations of these materials, forexample. Typical anode electrodes comprise a carbon material thatincludes a current collector such as a copper sheet. Carbon is oftenused because it has excellent electrochemical properties and is alsoelectrically conductive. Anode electrodes currently used in rechargeablelithium-ion cells typically have a specific capacity of approximately200 milliamp hours per gram. Graphite, the active material used in mostlithium ion battery anodes, has a theoretical energy density of 372milliamp hours per gram (mAh/g). In comparison, silicon has a hightheoretical capacity of 4200 mAh/g. In order to increase volumetric andgravimetric energy density of lithium-ion batteries, silicon may be usedas the active material for the cathode or anode. Silicon anodes may beformed from silicon composites, with more than 50% silicon, for example.Furthermore, the anode may comprise lithium, sodium, potassium, silicon,and mixtures and combinations thereof.

In an example scenario, the anode 101 and cathode 105 store the ion usedfor separation of charge, such as lithium. In this example, theelectrolyte carries positively charged lithium ions from the anode 101to the cathode 105 in discharge mode, as shown in FIG. 1 for example,and vice versa through the separator 105 in charge mode. The movement ofthe lithium ions creates free electrons in the anode 101 which creates acharge at the positive current collector 1078. The electrical currentthen flows from the current collector through the load 109 to thenegative current collector 107A. The separator 103 blocks the flow ofelectrons inside the battery 100, allows the flow of lithium ions, andprevents direct contact between the electrodes.

While the battery 100 is discharging and providing an electric current,the anode 101 releases lithium ions to the cathode 105 via the separator103, generating a flow of electrons from one side to the other via thecoupled load 109. When the battery is being charged, the oppositehappens where lithium ions are released by the cathode 105 and receivedby the anode 101.

The materials selected for the anode 101 and cathode 105 are importantfor the reliability and energy density possible for the battery 100. Theenergy, power, cost, and safety of current Li-ion batteries need to beimproved in order to, for example, compete with internal combustionengine (ICE) technology and allow for the widespread adoption ofelectric vehicles (EVs). High energy density, high power density, andimproved safety of lithium-ion batteries are achieved with thedevelopment of high-capacity and high-voltage cathodes, high-capacityanodes and functionally non-flammable electrolytes with high voltagestability and interfacial compatibility with electrodes. In addition,materials with low toxicity are beneficial as battery materials toreduce process cost and promote consumer safety.

The performance of electrochemical electrodes, while dependent on manyfactors, is largely dependent on the robustness of electrical contactbetween electrode particles, as well as between the current collectorand the electrode particles. The electrical conductivity of siliconanode electrodes may be manipulated by incorporating conductiveadditives with different morphological properties. Carbon black(SuperP), vapor grown carbon fibers (VGCF), and a mixture of the twohave previously been incorporated separately into the anode electroderesulting in improved performance of the anode. The synergisticinteractions between the two carbon materials may facilitate electricalcontact throughout the large volume changes of the silicon anode duringcharge and discharge.

State-of-the-art lithium-ion batteries typically employ agraphite-dominant anode as an intercalation material for lithium.Silicon-dominant anodes, however, offer improvements compared tographite-dominant Li-ion batteries. Silicon exhibits both highergravimetric (3579 mAh/g vs. 372 mAh/g for graphite) and volumetriccapacities (2194 mAh/L vs. 890 mAh/L for graphite). In addition,silicon-based anodes have a lithiation/delithiation voltage plateau atabout 0.3-0.4V vs. Li/Li+, which allows it to maintain an open circuitpotential that avoids undesirable Li plating and dendrite formation.While silicon shows excellent electrochemical activity, achieving astable cycle life for silicon-based anodes is challenging due tosilicon's large volume changes during lithiation and delithiation.Silicon regions may lose electrical contact from the anode as largevolume changes coupled with its low electrical conductivity separate thesilicon from surrounding materials in the anode.

In addition, the large silicon volume changes exacerbate solidelectrolyte interphase (SEI) formation, which can further lead toelectrical isolation and, thus, capacity loss. Expansion and shrinkageof silicon particles upon charge-discharge cycling causes pulverizationof silicon particles, which increases their specific surface area. Asthe silicon surface area changes and increases during cycling, SEIrepeatedly breaks apart and reforms. The SEI thus continually builds uparound the pulverizing silicon regions during cycling into a thickelectronic and ionic insulating layer. This accumulating SEI increasesthe impedance of the electrode and reduces the electrode electrochemicalreactivity, which is detrimental to cycle life.

An effective solution to improve the performance of silicon dominantanodes is to increase the electrical conductivity of the electrode aswell as protecting the surface of silicon particles by adding additivesto the slurry. These additives can improve the conductive pathways forelectrons, reduce the pulverization, and subsequently minimizingcapacity loss in electrode active materials and, thus, enhancing theoverall performance of silicon dominant anode batteries. To improve theperformance of the silicon-dominant anode batteries, a new class ofsilicon-containing organic compound has been synthesized and used as anadditive in silicon dominant anodes. This class of organopolymercomprises at least a silazane monomer and a silane monomer.

Combining the silazane and silane monomers can improve the thermalstability of these anode materials. The addition of this additive to theanode slurry significantly improves the cyclability of the battery,increases anode conductivity, and creates linear patterns in the anodewhich can help in reducing anode swelling.

FIG. 2 illustrates the general chemical structure of silosilazanes, inaccordance with an example embodiment of the disclosure. Referring toFIG. 2, there is shown silosilazane 200 comprising a silazane group 201and a silane group 203. The silazane monomer may comprise a hydride ofsilicon and nitrogen having a straight or branched chain of silicon andnitrogen atoms joined by covalent bonds, and the silane may comprise agroup of chemical compounds of silicon and other atoms such as carbon,nitrogen and hydrogen.

Silosilazanes may be synthesized by addition of an appropriate amount ofSiCl₄ to silanes in a diluent such as N-Methyl-2-Pyrrolidone (NMP)solution, which is a polar solvent. In one example, 0.5 grams of SiCl₄(0.33 ml) may be added to a solution of[3-(2-Aminoethylamino)propyl]trimethoxysilane (3.0 grams) in NMP (5grams) to form a colorless, transparent solution. The product is formedby releasing HCl gas through an exothermic reaction.

In another example, polysilosilazane may be synthesized by adding 13.82grams of SiCl₄ (9.3 ml) to a solution of[3-(2-Aminoethylamino)propyl]trimethoxysilane (36.82 grams) in NMP (50grams) in an ice bath to form an orange, translucent solution afterreleasing considerable amount of HCl gas.

FIG. 3A illustrates a process flow for fabricating a silicon-dominantanode with silosilazane additive, in accordance with an exampleembodiment of the disclosure. While conventional processes to fabricatecomposite electrodes physically mix the active material, conductiveadditive, and binder together and coat directly on a current collector,this disclosure employs a high-temperature pyrolysis process coupledwith a lamination process. After the raw electrode materials are mixed,they may be coated on a substrate. The active layer may then be thenpeeled into sheets, cut into desired size, cured, and then and undergonepyrolysis at high-temperature to form an anode coupon with high Sicontent. The anode coupon is then laminated on an adhesive-coatedcurrent collector.

This process is shown in the flow diagram of FIG. 3A, starting with step301 where the active material may be mixed with a binder/resin such aspolyimide (PI) or polyamide-imide (PAI), solvent, the silosilazaneadditive, and optionally a conductive carbon. In an example scenario,silicon powder (5-20 μm particle size, for example) may be dispersed inNMP and silosilazane solution with the amount of silosilazane being 1.2%with respect to silicon. Polyamic acid resin (15% solids in NMP) may beadded to the mixture at 500 rpm for 10 minutes, and further dispersedbetween 700-1000 rpm for several hours to achieve a slurry viscositywithin 1500-3000 cP (total solid content of about 30%).

In an example scenario, the silosilazane may comprise between 1% and 20%of the slurry. The silosilazane may comprise one or more amine groups.In another example scenario, the silosilazane may comprise anorganosilosilazane comprising amines and one or more silanols, silylethers, sylil chlorides, dialkylamoinosilanes, silyl hydrides, and/orcyclic azasilanes. After mixing the silosilazane with the silicon, theymay be referred to as silosilazane-treated silicon particles, which maycomprise silicon oxide surfaces reacted with the one or moreorganosilosilazanes.

In step 303, the slurry may be coated on a polymer substrate, such aspolyethylede terephthalate (PET), polypropylene (PP), or Mylar. Theslurry may be coated on the PET/PP/Mylar film at a loading of 3-4 mg/cm²(with 15% solvent content), and then dried to remove a portion of thesolvent in step 305. An optional calendering process may be utilizedwhere a series of hard pressure rollers may be used to finish thefilm/substrate into a smoothed and denser sheet of material.

In step 309, the green film may then be removed from the PET, where theactive material may be peeled off the polymer substrate, the peelingprocess being optional for a polypropylene (PP) substrate, since PP canleave ˜2% char residue upon pyrolysis. The peeling may be followed by acure and pyrolysis step 311 where the film may be cut into sheets, andvacuum dried using a two-stage process (120° C. for 15 h, 220° C. for 5h). The dry film may be thermally treated at 1175° C. to convert thepolymer matrix into carbon.

In step 313, the pyrolyzed material may be laminated on the currentcollector, where a 15 μm thick copper foil may be coated withpolyamide-imide with a nominal loading of 0.45 mg/cm² (applied as a 6 wt% varnish in NMP, dried 16 h at 110° C. under vacuum). Thesilicon-carbon composite film may be laminated to the coated copperusing a heated hydraulic press (50 seconds, 300° C., and 4000 psi),thereby forming the finished silicon-composite electrode.

The addition of silosilazanes to silicon-dominant (e.g., >50% silicon)anodes provides advantages such as decreased cell resistance, improvedcyclability, self-assembly patterns, and reduced swelling. The anodeactive material may comprise ridges formed in a manner consistent withself-assembly. These long ridges may provide a structural advantage inabsorbing the strain from swelling from silicon lithiation. The film maybe substantially held together by the partially or fully pyrolyzedcarbon film. The resulting film may be on the order of 10 to 100 μmthick and have a conductivity of 1 Siemen/cm (S/cm) or more. In anexample scenario, the anode active material may comprise 50-95% silicon.

FIG. 3B is a flow diagram of a process for direct coating electrodeswith silosilazane additive, in accordance with an example embodiment ofthe disclosure. This process comprises physically mixing the activematerial, conductive additive, and binder together, and coating itdirectly on a current collector. This example process comprises a directcoating process in which an anode slurry is directly coated on a copperfoil using a binder such as CMC, SBR, Sodium Alginate, PAI, PAA, PI andmixtures and combinations thereof. Another example process comprisingforming the active material on a substrate and then transferring to thecurrent collector is described with respect to FIG. 3A.

In step 351, the raw electrode active material may be mixed using abinder/resin (such as PI, PAI), solvent, and conductive carbon. Forexample, graphene/VGCF (1:1 by weight) may be dispersed in NMP undersonication for, e.g., 1 hour followed by the addition of Super P (1:1:1with VGCF and graphene) and additional sonication for, e.g., 45-75minutes. Silicon powder with a desired particle size, may then bedispersed in polyamic acid resin (15% solids in N-Methyl pyrrolidone(NMP)) at, e.g., 1000 rpm in a ball miller for a designated time, andthen the conjugated carbon/NMP slurry may be added and dispersed at,e.g., 2000 rpm for, e.g., another predefined time to achieve a slurryviscosity within 2000-4000 cP and a total solid content of about 30%.The particle size and mixing times may be varied to configure the activematerial density and/or roughness.

In step 353, the slurry may be coated on the foil at a loading of, e.g.,3-4 mg/cm², which may undergo drying in step 355 resulting in less than15% residual solvent content. In step 357, an optional calenderingprocess may be utilized where a series of hard pressure rollers may beused to finish the film/substrate into a smoother and denser sheet ofmaterial.

In step 359, the active material may be pyrolyzed by heating to 500-800C such that carbon precursors are partially or completely converted intoglassy carbon. The pyrolysis step may result in an anode active materialhaving silicon content greater than or equal to 50% by weight, where theanode has been subjected to heating at or above 400 degrees Celsius.Pyrolysis can be done either in roll form or after punching in step 361.If done in roll form, the punching is done after the pyrolysis process.The punched electrode may then be sandwiched with a separator andcathode with electrolyte to form a cell. In step 363, the cell may besubjected to a formation process, comprising initial charge anddischarge steps to lithiate the anode, with some residual lithiumremaining.

FIG. 4 illustrates a boxplot of anode conductivity of control anodes andanodes with silosilazane additive, in accordance with an exampleembodiment of the disclosure. Referring to FIG. 4, there is shown anodeconductivity plot 400 for control silicon-dominant anodes andsilicon-dominant anodes with silosilazane additive. As seen in the plot,the control anodes have a mean conductivity of 0.4041 S/cm, while thesilosilazane additive anodes have a mean conductivity of 1.977 S/cm,nearly five times higher, illustrating the improvement in conductivityresulting from silosilazane additives in silicon-dominant anodes.

FIG. 5 shows an optical image of a silicon-dominant anode withsilosilazane additive, in accordance with an example embodiment of thedisclosure. Referring to FIG. 5, there is shown an image of a topsurface of an anode. The current collector tab can be seen at the top ofthe image. The uniform patterns as indicated by the dashed lines may beas a result of the formation of a self-assembled silosilazane polymerduring high temperature heat treatments, the self-assembled polymers dueto specific interactions of hydrophilic and hydrophobic groups of thepolymer or the mutual incompatibility of macromolecular fragments withother anode slurry components such as silicon.

The dashed black lines in FIG. 5 show the direction of the patterns onthe anode. The width of the bare metal weldable tab is 7 mm and thepeak-to-peak distance between the ridges is of the order of 100 um to1000 um. These ridges may provide strain relief/absorption of strainfrom swelling of the anode during lithiation.

FIG. 6 illustrates cell swelling for control anodes and silosilazaneadditive anodes, in accordance with an example embodiment of thedisclosure. Referring to FIG. 6, there is shown the percentage of cellswelling measured at 80% of capacity. For the first two bars of thechart, the cells were charged to 4.2V at a 2 C rate and discharged to2.75 V at 0.5 C rate, while the third and fourth bars show swelling forcells charged to 4.2V at a 4 C rate and discharged to 3.1V at 0.5 C. Asshown in the plot, the control anode cell swells 8.46% and 9.23%compared to 5.42% and 5.83% for the silosilazane additive anode cell.This may be due to the presence of patterns on the anode, such as thoseshown in FIG. 5, that provide a void space for silicon expansion andcontraction during cycling.

FIG. 7 illustrates cycling performance for control silicon-dominantanode cells and silosilazane additive silicon-dominant anode cells, inaccordance with an example embodiment of the disclosure. Referring toFIG. 7, the plot compares the cycling performance of the standard anode(control) with silosilazane anodes (solid lines) at a charge rate of 1 Cand discharge rate of 0.5 C between 4.2-3.1 volts. The result shows thataddition of the silosilazane improves the performance of the standardanode, with the normalized capacity of the silosilazane anode cellsdemonstrating higher capacity through ˜600 cycles with 80% of capacityremaining while the control anodes drop to 80% at ˜460 cycles.

FIG. 8 illustrates cycling performance with higher charge rate forcontrol silicon-dominant anode cells and silosilazane additivesilicon-dominant anode cells, in accordance with an example embodimentof the disclosure. Referring to FIG. 8, the plot shows galvanostaticcycling performance of silicon-dominant anodes (control) versus thesilosilazane anode at 2 C-charge and 0.5 C-discharge between 4.2-2.75volts. The result shows that the addition of the silosilazane improvesthe performance of the standard anode, with the normalized capacity ofthe silosilazane anode cell demonstrating higher capacity through ˜250cycles with 80% of capacity remaining while the control anodes drop to80% after ˜160 cycles.

FIG. 9 illustrates cycling performance with a 4 C charge rate forcontrol silicon-dominant anode cells and silosilazane additivesilicon-dominant anode cells, in accordance with an example embodimentof the disclosure. Referring to FIG. 9, the plot compares the cyclingperformance of the silicon-dominant control anodes (control) withsilosilazane anode cells at a charge rate of 4 C and discharge rate of0.5 C between 4.2-3.1 volts. The result shows that addition of thesilosilazane improves the performance of the standard anode, with thenormalized capacity of the silosilazane anode cell demonstrating highercapacity through ˜450 cycles with 80% of capacity remaining while thecontrol cells drop to 80% after ˜410 cycles.

FIG. 10 illustrates cell performance with anodes comprising siliconpretreated with polysilosilazane, in accordance with an exampleembodiment of the disclosure. Referring to FIG. 10, there is shown cycleperformance of cells where silicon in the anodes was pretreated withpolysilosilazane by a pyrolysis procedure.

In this example, silicon may be pyrolyzed at 1100-1200° C. withpolysilosilazane and NMP for 45-75 minutes. The pretreated silicon maybe ball milled and used in a standard anode slurry. This treated slurry,as well as a standard slurry without polysilosilazane, are used tofabricate 5-layer pouch cells, and the cells are cycled at 4 C chargeand 0.5 C discharge between 4.2-3.1 V for the data shown in FIG. 10. Asseen in the plot, the cells with polysilosilazane treated anodesdemonstrate better cycle life as compared to control cells.

Different concentrations of polysilosilazanes with respect to the weightpercentage of silicon may be utilized, and excellent performance may beobtained from cells built using anodes with 1% polymer pretreatedsilicon. The adoption of the pretreatment process allows ease duringmixing process since there is no bare polymer in the slurry, therebyavoiding gelling. This process can also be used to couplepolysilosilazane pretreated silicon with AEAPTMS additive to getenhanced conjugation between the silicon and carbon in the system.

FIG. 11 illustrates material characterization data for apolyorganosiloxane additive silicon-dominant anode, in accordance withan example embodiment of the disclosure. Referring to FIG. 11, there isshown x-ray diffraction data for a polysiloxane resin after pyrolyzing.Silicon oxycarbides are ceramics that have chemical structures withsilicon bonded to both oxygen and carbon simultaneously. In an examplescenario, anodes comprise polymer and metal oxide/ceramic coatingapplied in combination with polyorganosiloxane/SiOC.

Polyorganosiloxane resin converts to oxycarbide and/or silicon carbideupon heat treatment at 1150-1250° C. under an argon atmosphere. Thex-ray data in FIG. 11 demonstrates the conversion of polyorganosiloxaneto silicon oxycarbide. Silicon oxycarbide can be suspended within theanode matrix or coated on to the surface of the Si anode. The peaks inthe x-ray data illustrate the presence of SiOC/SiO_(x), SiOC, and SiC.The carbonized product of organopolysiloxane resin is less crystallineand shows broad x-ray peaks in the x-ray data of FIG. 11, whichcorrespond to SiOC and SiC peaks, which is an indication of theformation of SiOC+SiC mixture under high temperature pyrolyzingconditions. However, nanocrystalline SiC can also form during a heattreatment process.

The pyrolysis process of polymeric resin precursors results in carbonincorporation to SiO₂ to form SiOC. The composition of the siliconoxycarbides may be varied from 1 to 20% by weight of thesilicon-dominant anode active material and the polymerization of thismaterial may range up to a molecular weight of 6000, or 6 kDa where Dais dalton (1 Da=1 g/mol). The low density (2.1 g/cm³) and open structureof SiOC structures enable high gravimetric capacity with high charge anddischarge rates. The electrochemical capacity in SiOC is mainly due toreversible Li-adsorption in the disordered carbon phase and not theconventional alloying reaction similar to Si. Thus, incorporation ofSiOC can significantly improve efficiency of Li ion incorporation to Si.Finally, graphite may be added to the anode in addition to thepolyorganosiloxane so that the final anode contains bothgraphite/graphene and SiOC, where the graphite/graphene maysignificantly improve the conductivity of the silicon layer.

FIG. 12 illustrates electrode conductivity for various silicon-dominantanodes with added silicon oxycarbides, in accordance with an exampleembodiment of the disclosure. Referring to FIG. 12, there is shownconductivity measurements for a standard silicon-dominant anode and foranodes with 1%, SiOC, 5% SiOC, and 10% SiOC. As shown in theconductivity plot, the conductivity of the silicon-dominant anode isimproved by adding silicon oxycarbides. Additionally, incorporation ofSi—C—Si bonds can promote the formation of conductive islands within theelectrode matrix or on the surface of Si particles. The 10% SiOC anodedemonstrates ˜0.45 S/cm as compared to ˜0.28 S/cm for a control anode.

FIG. 13 illustrates cyclic voltammetric analysis of half coin cells fordifferent SiOC compositions, in accordance with an embodiment of thedisclosure. Referring to FIG. 13, there is shown current density versusvoltage measurements at the 4th cycle (left) and 7^(th) cycle (right).The presence of SiOC increased the current response in the cyclicvoltammetric studies. Anodes prepared with Si+SiOC do not showsignificant redox peak shift (hysteresis) compared to the standard Si(labeled Si) anode after cycling. This is mainly due to the improvedconductivity on the surface of silicon, which can also be beneficial forfast charging performance.

FIG. 14 illustrates capacity retention of silicon-dominant anodes withpolyorganosiloxane and control anodes, in accordance with an exampleembodiment of the disclosure. Referring to FIG. 14, there is showncapacity retention plots for silicon-dominant anodes as well assilicon-dominant anodes with 2% and 5% polyorganosiloxane. Compared tothe Si control anode, the introduction of SiOC improved the overallcycle life performance of composite Si anodes at a 4 C charge rate with˜10% greater capacity than the control anodes after 300 cycles.

FIG. 15 illustrates conductivity of silicon-dominant control electrodesand electrodes with cyclic silosiloxane, in accordance with an exampleembodiment of the disclosure. For these anodes, a cyclic silosiloxane(1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane) 20% wasadded to a solution of silane (AEAPTMS; 35%) and NMP (45%) to form asilane-siloxane solution. Additions of >20% siloxane may lead to theformation of non-soluble materials in the solution.

In an example scenario, 1 gram of this solution may be added to 6-7grams of silicon, 8-10 grams of NMP and 14-18 grams resin, and thenmixed to form a slurry with a viscosity of 5000 cp. This slurry wascoated on PET, peeled, and treated at 1175° C. under argon gas to form afree-standing silicon dominant electrode film. The film was laminated oncopper foil.

Referring to FIG. 15, the conductivity measurements shows theconductivity of the electrode versus control (without silane-siloxaneadditive) where the silane-siloxane anode is demonstrated to have betterelectronic conductivity than the control, with conductivity between 2and 3 times higher than the control. Another possible additive materialis cyclic 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl cyclotetrasiloxane,which may be utilized to increase anode conductivity.

FIG. 16 illustrates cell performance for silicon-dominant anodes withpolydimethylsiloxane as an additive, in accordance with an embodiment ofthe disclosure. Referring to FIG. 16, there is shown normalizeddischarge capacity for anodes with polydimethylsiloxane (PDMS) as anadditive and control anodes. To form the PDMS additive anode, siliconpowder may be treated with PDMS at high temperature e.g., >1000° C.,under an argon atmosphere. In one example, the ratio of PDMS to siliconis approximately 1:1. The product may be crushed and milled into apowder to be used as the silicon source in a slurry comprising 32%solvent, 20 percent silicon, and 48 percent resin. This slurry may becoated on PET, peeled, and treated at 1175° C. under argon gas to form afree-standing silicon-dominant electrode film, which may then belaminated on copper foil. FIG. 16 shows the performance of the cell withPDMS-treated silicon anode (75% silicon) versus two controls. Control 1contains 85% silicon and control 2 contains 75% silicon. The plot showsthat there is some improvement in cycle life with PDMS as an additive insilicon-dominant anodes.

In an example embodiment of the disclosure, a method and system isdescribed for silosilazanes as additives for silicon-dominant anodes ina battery that may include a cathode, an electrolyte, and an anodeactive material. The active material may comprise 50% or more siliconand an additive comprising one or more of: silosilazane, siliconoxycarbides, and polyorganosiloxane. The silosilazane may comprise oneor more amine groups. The silosilazane may comprise one or more of:silanols, silyl ethers, sylil chlorides, dialkylamoinosilanes, silylhydrides, and cyclic azasilanes. The active material may comprise a filmwith a thickness between 10 and 80 microns. The film may have aconductivity of 1 S/cm or more. The active material may comprise between50% and 95% silicon. The active material may be held together by apyrolyzed carbon film. The anode may comprise lithium, sodium,potassium, silicon, and/or mixtures and combinations thereof. Thebattery may comprise a lithium ion battery. The electrolyte maycomprises a liquid, solid, or gel.

As utilized herein the terms “circuits” and “circuitry” refer tophysical electronic components (i.e. hardware) and any software and/orfirmware (“code”) which may configure the hardware, be executed by thehardware, and or otherwise be associated with the hardware. As usedherein, for example, a particular processor and memory may comprise afirst “circuit” when executing a first one or more lines of code and maycomprise a second “circuit” when executing a second one or more lines ofcode. As utilized herein, “and/or” means any one or more of the items inthe list joined by “and/or”. As an example, “x and/or y” means anyelement of the three-element set {(x), (y), (x, y)}. In other words, “xand/or y” means “one or both of x and y”. As another example, “x, y,and/or z” means any element of the seven-element set {(x), (y), (z), (x,y), (x, z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means“one or more of x, y and z”. As utilized herein, the term “exemplary”means serving as a non-limiting example, instance, or illustration. Asutilized herein, the terms “e.g.,” and “for example” set off lists ofone or more non-limiting examples, instances, or illustrations. Asutilized herein, a battery, circuitry or a device is “operable” toperform a function whenever the battery, circuitry or device comprisesthe necessary hardware and code (if any is necessary) or other elementsto perform the function, regardless of whether performance of thefunction is disabled or not enabled (e.g., by a user-configurablesetting, factory trim, configuration, etc.).

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A battery, the battery comprising: a cathode, anelectrolyte, and an anode comprising an active material, the activematerial comprising: silicon particles; and an additive comprisingsilosilazane wherein said silosilazane comprises one or more aminegroups and one or more of: silyl chlorides, dialkylaminosilanes, andcyclic azasilanes.
 2. The battery according to claim 1, wherein theactive material comprises a film with a thickness between 10 microns and80 microns.
 3. The battery according to claim 1, wherein the activematerial is held together by a pyrolyzed carbon film.
 4. The batteryaccording to claim 1, wherein the anode comprises lithium, sodium,potassium, silicon, and/or mixtures and combinations thereof.
 5. Thebattery according to claim 1, wherein the active material comprises acoating comprising one or more of: a metal oxide, a ceramic, and apolymer.
 6. The battery according to claim 1, wherein the electrolytecomprises a liquid, solid, or gel.
 7. A method of forming a battery, themethod comprising: forming a battery comprising an anode, a cathode, andan electrolyte, the anode comprising a silicon-dominant active materialthat comprises silicon particles and an additive comprisingsilosilazane; wherein said silosilazane comprises one or more aminegroups and one or more of: silyl chlorides, dialkylaminosilanes, andcyclic azasilanes.
 8. The method according to claim 7, wherein thesilicon-dominant material is formed by coating a substrate with a slurrycomprising a carbon binder, silicon particles, and silosilazane.
 9. Themethod according to claim 7, wherein the active material comprises afilm with a thickness between 10 microns and 80 microns.
 10. The methodaccording to claim 7, wherein the active material is held together by apyrolyzed carbon material.
 11. The method according to claim 7, whereinthe active material comprises a coating comprising one or more of: ametal oxide, a ceramic, and a polymer.
 12. An anode for a battery, theanode comprising: an active material on a conductive current collector,wherein the active material comprises: silicon particles; carbon; and anadditive comprising silosilazane; wherein said silosilazane comprisesone or more amine groups and one or more of: silyl chlorides,dialkylaminosilanes, and cyclic azasilanes.